The Art of the Helicopter John Watkinson - Karatunov.net

Fig. 6.16 The complex fuel system of the CH-47. See text.
Engines and transmissions 223
Each main tank supplies the engine on the same side, but there is also a cross feed line
between the engines so that both can run from one main tank. This line can be closed
by the pilot to prevent fuel loss in case of major damage at one side of the machine.
6.18 The turbine engine
The turbine engine is a more recent development than the piston engine. Although the
idea is older than the piston engine, the first aircraft turbines were not perfected until
much later when the necessary materials were available. Whittle in England and von
Ohain in Germany independently developed practical turbine engines during World
War II.
The Otto cycle or four-stroke piston engine draws charge in through a throttle, compresses
it, burns it to release power and then exhausts. In the Diesel engine only air is
drawn in and compressed, and the fuel is injected directly into the cylinder. There is no
throttle, and the power is controlled by the amount of fuel injected. Detonation cannot
occur, and low octane fuel can be used. In a piston engine the four phases are conducted
sequentially on a fixed quantity of charge in the same cylinder. The turbine is like a
continuous version of a Diesel engine. Instead of operating on charge one phase at a
time in the same place, charge passes through the machine continuously and the four
phases take place at different points in the machine. Like the Diesel, the turbine can
use low octane fuel and generally runs on AVTUR which is basically kerosene. Also
like the Diesel engine, the power developed by a turbine engine is controlled by the
amount of fuel fed to the burners.